The objective of this proposal is to further our understanding of the biology and regulation of P element, a transposable element found in Drosophila melanogaster. P elements are particularly interesting because their transposition is both genetically regulated (the P-M hybrid dygenesis syndrome) and tissue specific (transposition only occurs in the germline and not in somatic tissues). Recently we have shown that the germline specificity of P element transposition is regulated at the level of mRNA splicing. As a continuation of these studies we will: (1) Determine to the nucleotide which cis-acting sequences of the P element pre-mRNA transcript are required for the germline specificity. (2) Determine the spatial and developmental profile of the P element germline specific splice using a beta gal staining assay. (3) Genetically screen for mutants in the gene encoding the germline specific RNA splicing factor. (4) Attempt to isolate and maintain a Drosophila germline cell line that is capable of splicing the P element germline specific intron. (5) Attempt to establish an in vitro splicing system that will allow the biochemical identification and purification of the germline specific RNA splicing factor. (6) Identify which protein product(s) of P element encode the P cytotype repressor, (7) Determine the mechanism by which the P cytotype repressor functions.